Have been using Kindle Unlimited for a couple of years at least. We consider the service to be worth the price.
I think Kindle Unlimited is similar to Netflix in the sense that, if you’re looking for a specific book you want to read, you’re probably going to be disappointed. But if you keep your mind open to things you wouldn’t ordinarily read, or things you’ve never heard of, you can find some gems.
There is plenty of crap in the self-published world, but you find that same crap for sale outside of Kindle Unlimited too. Any part of reading is separating the wheat from the chaff. There is plenty of traditionally published dreck out there in the bookstores, some of it even very popular.
FWIW, I’m reading Slaughterhouse Five on Kindle Unlimited right now. Not crap. I’ve also enjoyed some great historical stuff – a series of short autobiographical stories on WWII called The Good War and an excellent book about the dust bowl crisis called The Worst Hard Time.